The embodiments of the present invention apply to the taxiing of an aircraft, in particular a civil or military aeroplane for transporting passengers or cargo (freight), or also a drone. It relates more particularly to the generation of a yawing moment (about the vertical axis of the aircraft) enabling the lateral control of the taxiing aircraft.
In the context of the embodiments of the present invention, taxiing is understood to mean any type of movement on the ground which is possible for an aircraft, such as movement on a landing runway during landing and takeoff phases, or movement on taxiways or on manoeuvring areas, in particular. Currently, the pilot controls the lateral movements of the aircraft on the ground with the aid of manual control elements (for example a handwheel enabling the orientation of the front landing gear wheel, a joystick for controlling the thrust of the engines, brake pedals, a rudder), along a course on the ground. These control elements enable control of actuators of the aircraft capable of influencing the lateral movements of the aircraft, essentially with the orientation of the nose wheel (and optionally the orientation of the tail gears) and the tail fin rudder, and more rarely, via an asymmetrical use of the engines and brakes.
Within the context of the embodiments of the present invention, a front wheel is understood to mean a mechanical assembly being provided with at least one wheel which is situated at the front of the aircraft, which preferably forms part of a front landing gear of the aircraft, and which can be oriented so as to be able to move the aircraft laterally when the aircraft is taxiing. In the event of breakdown of the orientation system of the nose wheel, at low speed, the aircraft can no longer be controlled laterally with the aid of the usual control elements for controlling the trajectory. In this case, generally, the system of orientation is deactivated and the nose wheel is free to rotate (“free to castor” mode).
In order to remedy this problem of control, the document FR-2 929 019 discloses a device which makes it possible to control the aircraft on the ground according to the lateral axis in such a situation by automatically applying a differential (or asymmetrical) braking in order to generate a yawing moment, in response to a control command on the usual steering control elements. To this end this document FR-2 929 019 provides an emergency BSF function (“backup steering function”) for directional control, which is such that the behaviour of the aircraft is as close as possible to that obtained in normal conditions, when the system of orientation of the nose wheel is available.
The application of such differential braking, which therefore makes it possible to generate a yawing moment in the event of breakdown of the system of orientation of the nose wheel, nevertheless results in a loss of speed of the aircraft. As this loss of speed is higher than that usually obtained when the normal steering system is available, it may make the control more delicate. The pilot should, in fact, adapt the thrust to the braking applied by the BSF function upon initiation, but likewise during turning or when exiting the turn. Moreover, once the turn is established, slight corrections by the pilot on the control elements may result in a braking and therefore variable deceleration.
If the thrust applied by the pilot in the turn is not adapted to counter the variation in speed generated by the BSF function, there is a risk of the aircraft stopping or of the turn being effected at too great a speed. In the case of stopping, the nose wheel may reach a substantial turning angle, or in rare cases may even touch its mechanical stop, which may result in maintenance actions, associated in particular with the risk of damage to the orientation system of the nose wheel. In addition, if the aircraft stops with a substantial turning angle of the nose wheel or even at the edge of the runway, restarting may be quite difficult.
On the other hand, if the management of the thrust results in an overspeed, the performance produced by the braking may be limited relative to the requirement. Furthermore, once the turn is effected, the pilot will have to reduce the thrust, so that once the aircraft is in a straight line, when the BSF function no longer applies braking, the aircraft retains an operational speed.
The difficulty associated with the control of the speed during the use of the BSF function also resides in the fact that the response time of the engines close to the idle speed is long, compared to the effect of the braking which is much more dynamic. The task of pilot control with a view to maintaining the speed may then become delicate because of this difference in dynamics between the braking and the engine thrust. Thus the BSF function, which therefore makes it possible to implement the lateral control of the aircraft in the event of breakdown of the nose wheel orientation system, is capable of generating variations in speed.
In view of the foregoing, at least one object is to remedy this drawback. In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.